(IJACSA) International Journal of Advanced Computer Science and Applications, Vol. 10, No. 5, 2019 Frequency Reconfigurable Vivaldi Antenna with Switched Resonators for Wireless Applications 1 4 Rabiaa Herzi , Ali Gharsallah Mohamed-Ali Boujemaa2, Fethi Choubani3 Unit of Research CSEHF Faculty of Sciences of Tunis INNOVCOM Laboratory, SUPCOM, University of El Manar, Tunis 2092, Tunisia Carthage, Tunis, Tunisia Abstract—In this paper, a frequency reconfigurable Vivaldi There are many types of frequency reconfigurable antenna with switched slot ring resonators is presented. The antennas such as switching between different narrow bands, principle of the method to reconfigure the Vivaldi antenna is wideband to notch band reconfiguration, wideband to based on the perturbation of the surface currents distribution. narrowband switching [10-11]. Switched ring resonators that act as a bandpass filter are printed in specific positions on the antenna metallization. This structure Achieving an antenna which has the capacity of wideband has the ability to reconfigurate between wideband mode and four to multi-narrow bands reconfiguration is very important and narrow-band modes which cover significant wireless essential for several applications such as a cognitive radio that applications. Combination of the bandpass filters and tapered uses wideband sensing and multi-bands communications [10, slot antenna characteristics achieve an agile antenna capable to 12, 13]. operate in UWB mode from 2 to 8 GHz and to generate multi- narrow bands at 3.5 GHz, 4GHz, 5.2 GHz, 5.5 GHz, 5.8 GHz and Because of their better radiation performances as well as 6.5 GHz. The measurement and simulation results show good Ultra-wide bandwidth, elevated gain, and compact structure agreement. This antenna is an appropriate solution for wireless [14-15], Vivaldi antenna is the best selection to be used in applications which require reconfigurable Wideband multi- wideband to multi-bands reconfiguration. narrow bands antenna. Developing of reconfigurable antenna between wideband Keywords—Frequency reconfigurable; Vivaldi Antenna (VA); and multiple narrow-bands has received considerable Ultra-Wideband (UWB); slot ring resonator; wireless applications attention. In [16] and [17] two different switchable Vivaldi antennas have been investigated where several PIN diodes and I. INTRODUCTION capacitors are used which augment the complexity of the antenna design. In addition, the reconfigurability of both Research in antenna development has attracted many antennas has notably deteriorated the antenna gain which has researches to satisfy the requirements of modern wireless decreased by about 2.5 dBi. A reconfigurable Vivaldi antenna applications such as developing active, compact and was designed in [18], where the obtained agile narrow bands miniaturized antennas that can group many services [1-3]. are close with inconstant radiation patterns over the operating Developing of radio systems for multimode terminal frequency range. A wideband frequency agile patch antenna is applications which involve a combination of Wi-Fi, WLAN, proposed in [19]. The reconfigurability is achieved using Wimax, Bluetooth… is obligatory [4,5]. So, using systems Varactors which require high bias voltages. Very close with frequency reconfigurable operation and wideband frequency reconfigurable bands are attained from 1.47 to 1.84 spectrum sensing is a suitable solution due to its compactness, GHz. flexibility and its capability to operate over multiple bands [5- In this paper, a frequency reconfigurable Vivaldi antenna 6]. for wireless applications that has the capacity to switch from The reconfigurable antenna is an antenna which has the an UWB of 2-8 GHz to essential narrow bands is proposed. capability to change dynamically its radiation characteristics By inserting of switchable slot ring resonators using PIN such as its radiation patterns, frequency operations or its diodes, several narrow bands are obtained. In Section 2, polarization [7-8]. Usually, the reconfigurability of antenna is details of the UWB antenna and the proposed antenna design achieved using PIN diodes, Varactors or MEMS to change its are described. The principle of the method used to achieve a geometrical characteristics [1,4]. wide to narrow-bands reconfigurable Vivaldi antenna is demonstrated in Section 3. In Section 4, the simulated and Because of their benefits of flexibility, the capability to measured results obtained throughout the switch modes are reduce interferences and compactness, frequency explained and discussed. Finally, Section 5 presents the reconfigurable antenna is a better alternative which can be conclusion of this paper. used in cognitive radio and multi-mode applications [9]. More precisely, they are many modern systems which have great II. UWA AND RECONFIGURABLE ANTENNAS DESIGN numbers of antennas that are operated at different frequencies. Therefore, frequency reconfigurable antenna, which can The basic structure of the proposed antenna, which is support many functions at various frequencies bands and can shown in Fig. 1(a) is an UWB Vivaldi antenna that operates significantly decrease the hardware cost and size, is required. from 2 to 8 GHz. It consists of an exponentially tapered slot 414 | P a g e www.ijacsa.thesai.org (IJACSA) International Journal of Advanced Computer Science and Applications, Vol. 10, No. 5, 2019 printed on an FR-4 substrate that has 4.7 of permittivity and frequencies that correspond to a quarter of the wavelength 1.575 mm of thickness. It is fed by a microstrip line printed on (λ/4), while double serial ring slots act as pass band filter the other side of the substrate. The dimension of the antenna is which pass frequencies corresponding to a half wavelength L= 85 mm and W=70 mm. The exponential edge of the (λ/2). Then, the resonance current path length (D) the stop aperture antenna is determined using next equations: band and pass band filters can be expressed respectively as following: Where f, ( , ) and ( , ) (1) (4) (2) (5) (3) The resonance frequencies of the stop band and pass band Are respectively the exponential factor, the peak point and filters can be determined as follows: the bottom point of the exponential edge. (6) Fig. 1(b) shows the wide-narrow bands agile antenna √ configuration. The Vivaldi antenna geometry is modified by inserting four slot resonators at specific positions in order to (7) √ perturb the surface currents flow. Each resonator is formed by two symmetric ring slots connected by a rectangular gap. So, Where c, ℇeff, P and S are, respectively, the velocity of three pairs of ring slots are printed on the antenna light in the free space, the effective permittivity of the metallization and coupled into the tapered slot through four substrate, the perimeter of the ring slot which is equal to 31.4 pairs of gaps with 1 mm of width. The outer and the inner mm and the width of the split. radius of the ring slots are respectively 5 mm and 3 mm. Fig. 2 and Fig. 3 illustrate the structure and the response of Moreover, ten PIN diodes are inserted in the opening of the a single and double rings slot resonator. It is clear that the perturbing slots to switch the function of the different single slot ring resonator products a stop band response resonators and control the current distributions. around 2.14 GHz while the double rings resonator offers a pass-band filter at 3.65 GHz. The equivalent circuit of the double slot rings resonators which consists of two associated stop band filters is shown in Fig. 4. Two LC circuits are connected in series, where each LC circuit shows a stop band filter. (a) (b) Fig. 1. Simple Vivaldi Antenna (a) and Reconfigurable Vivaldi Antenna with PIN Diodes (b). (a) III. PRINCIPLE OF RECONFIGURATION OF THE VIVALDI ANTENNA The Ultra-Large Band that characterizes the Vivaldi antenna is the result of the tapered slot geometry that can be devised into two parts named the propagation and radiation parts. The propagation part guides the waves to the radiation area. Each level of the radiation part radiate at the corresponding frequency, where the width of the slot is about the half wavelength. Generally, frequency reconfigurable Vivaldi antenna can be achieved by disturbing the surface currents flow which is attained by distorting the inner edges of the tapered slot. Moreover, inserting slot ring resonator can act as a filter (b) which has the capability to pass a frequency band and block Fig. 2. Configuration of Single Ring Slot Resonator (a) and the S- others. Single ring slot acts as a stop band filter, blocking the Parameters Response (b). 415 | P a g e www.ijacsa.thesai.org (IJACSA) International Journal of Advanced Computer Science and Applications, Vol. 10, No. 5, 2019 blocks others. In this way, four modes are investigated. Fig. 7 shows four proposed structures with different positions of the printed resonator. Fig. 8 compares the reflection coefficients of the different structures where four narrow-band modes are achieved. (a) (a) (b) Fig. 5. Surface Currents Distribution of (a) the Simple Vivaldi Antenna and (b) (b) Vivaldi Antenna with Annular Slots at 3.5 GHz. Fig. 3. Configuration of Double Rings Slot Resonator (a) and the S- Parameters Response (b). Fig. 4. Equivalent Circuit of the Double Rings Slot Resonator. To investigate the effects of the slots ring resonator in the radiation characteristics of the Vivaldi antenna, a double rings slot resonator is inserted in the beginning of the radiation part. Fig. 6. Reflection Coefficients of the Antenna with and without Fig. 5 presents the surface currents distribution of the Vivaldi Perturbation. antenna with and without printed resonator. It can be seen that the current before inserting perturbation follows the direction of the inner radiation edges of the antenna. On the other hand, the surface current is distorted by inserting of the ring slots; it is significantly reduced along the inner edges. So the major asset of this method resides in the capability to promote the disruption of the currents in the annular slots and stopped its repartition along the radiation edges situated after the disturbance.